Abstract

Isocitrate lyase (EC 4.1.3.1) from mixed larval populations of Caenorhabditis elegans was stabilized
in crude extracts by centrifugation over a 0.2-0.6 Msucrose gradient for 2.5 hr in a vertical rotor (VTi 50) at
210,000g.The peak fractions from this sucrose gradient showed a half-life of 33 hr at 30 C and 225 hr at 4 C in
contrast to 2.5 and 52 hr, respectively, for the crude extract. A purification scheme involving
(NH4)2SO4 precipitation and chromatography on Sepharose
6B and diethylaminoethyl-cellulose yielded isocitrate lyase that gave one band after electrophoresis in a sodium
dodecyl sulfate-gel polymerized from 12% acrylamide. The purified enzyme with a molecular weight of 250,000
and subunit molecular weight of 61,600, had a specific activity of 2 μ moles glyoxylate formed
min-1 mg protein-1, and was obtained in a 4% yield. Isocitrate lyase from C.
elegans lost 80-85% of its activity in the precipitation by 33-55%
(NH4)2SO4, but this step appeared to be necessary for
purification to homogeneity. The use of fast protein liquid chromatography appeared to be promising in that it
provided an enzyme preparation that was about 50% pure with a specific activity as high as 3 μmoles
glyoxylate formed min-1 mg protein-1. Poly(A+)RNA was isolated from C.
elegans and translated in wheat germ cell-free system. Analysis on a 10% sodium dodecyl
sulfate-polyacrylamide gel showed varied translation products including one or more 60,000-Da
polypeptides.